Protection Of Tetradecyl 2,3-dihydroxybezoat Against White Matter Damage Induced By Chronic Cerebral Hypoperfusion

Background: Approximately 30-40% of dementia patients have vascular dementia(Va D)pathologies.Subcortical ischemic vascular dementia(SIVD)is a prevalent vascular dementia subtype that is often caused by small vessel disease resulting in chronic cerebral hypoperfusion.It has been estimated that most cases of SIVD,including Binswanger's disease,are frequently observed in patients with hypertension or atherosclerosis,as well as in the elderly population.The pattern of damage in SIVD has devastating consequences for progressive demyelination,lacunar infarcts,white matter rarefaction and progressive decline in cognitive function.Although acetylcholinesterase inhibitors and vasodilators show modest clinical significant effects on SIVD,there is no highly effective therapeutic approach.Our previous reports have shown that 11 novel alkyl benzoates(gentisides A-K)of traditional Chinese medicine,Gentiana rigescens Franch,have notable neuritogenic effect.Tetradecyl 2,3-dihydroxybenzoate(ABG-001),one of a series of synthesized novel gentisides derivatives,displayed the highest neuritogenic activity against PC12 cells of all synthesized compounds by activating the insulin-like growth factor-1(IGF-1)signaling pathway.Oral treatment with ABG-001 improves growth of newborn cells by the tropomyosin receptor kinase A(Trk A)in hippocampal dentate gyrus,proposing it might be absorbed and passed the blood brain barrier to persuade pro-neurogenesis effect.However,the effect of ABG-001 on white matter damage is still unknown.Therefore,the present study explored the effects of ABG-001 on white matter damage and cognitive deficits in a SIVD experimental model.Since both IGF-1 receptor(IGF-1R)and Trk A have been reported to be associated with the pharmacological action of ABG-001,we investigated the receptor involved in the effect of ABG-001.Methods: Cerebral hypoperfusion was induced in anesthetized male C57BL/6J mice by occluding the right unilateral common carotid artery(r UCCAO).The effect of ABG-001 on white matter damage and cognitive function was evaluated by immunohistochemistry,Morris water test and novel object recognition test.The exposure of immortalized mouse oligodendrocytic cell line(Oli-neu)or primary oligodendrocyte to oxygen glucose deprivation(OGD)was used as an in-vitro model to explore the protective effect of ABG-001 and to evaluate whether IGF-1R or Trk A in oligodendrocytes was involved in the action of ABG-001.Molecular docking was carried out to determine the binding free energy and binding mood of ABG-001 against the potential target receptors,IGF-1R and Trk A,using their co-crystallized ligands(alpha-l-fucose,FUC and 4-tert-butyl-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide,KWY,respectively)as references.The potential toxic effect of chronic treatment with ABG-001 was studied through the biochemical and hematological parameters investigation and the histological assessment.Results: ABG-001 significantly alleviated the reduced myelin basic protein(MBP)expression,oligodendrocyte loss and axonal damage at four weeks after r UCCAO,demonstrating protection against white matter damage after chronic cerebral hypoperfusion.Mice treated with ABG-001 showed significantly higher levels of myelinated axons and raised the proportion of thick myelinated axons substantially,rather than the thin myelinated axons.It suggests that ABG-001 has the potential to attenuate demyelination,rather than the remyelination,to achieve myelin integrity around axons.Also,the cognitive impairments in Morris water test and novel object recognition test after chronic brain hypoperfusion model were effectively relieved by treatment with ABG-001.Although,ABG-001 had no effect on oligodendrocyte precursor cell(OPC)number in the corpus callosum at the early-stage(3 d)of chronic hypoperfusion,ABG-001 ameliorated the oligodendrocyte apoptosis.Docking against IGF-1R indicated that ABG-001 has better binding energy than FUC,the co-crystallized ligand of IGF-1R,and exhibited an interaction closely similar in respect to FUC.Whereas,docking against Trk A exhibited that ABG-001 had a binding mode for Trk A,which was slightly different from the co-crystallized ligand of Trk A(KWY).It suggests that ABG-001 displayed high affinity for IGF-1R,but not for Trk A.Moreover,in vitro data exhibited that ABG-001 significantly improved oligodendrocyte(differentiated Oli-neu cells)survival in a concentration-dependent manner,but had no effect on the OPC cell line(Oli-neu)survival after OGD.Besides,ABG-001 did not promote viability of oligodendrocyte(differentiated Oli-neu cells)without OGD exposure.ABG-001 also significantly attenuated primary oligodendrocyte damage,as evidenced by the reduction of apoptotic cells.IGF-1R antagonist picropodophyllin(PPP)and short hairpin RNA(sh RNA)-mediated knockdown of IGF-1R revoked the ABG-001's protection on OGD-elicited oligodendrocyte damage.However,Trk A antagonist GW441756 had no effect on ABG-001's protection.We also examined whether IGF-1R is involved in the ABG-001's protection on oligodendrocytes in mice model of cerebral hypoperfusion.Our data showed that PPP completely reversed the protection mediated by ABG-001 against oligodendrocyte damage at the early stage of cerebral hypoperfusion.ABG-001 did not produce any mortality or toxicity symptoms throughout the study period.Chronic treatment with ABG-001 did not considerably affect the renal or hepatic functions when compared to control mice.ABG-001 had no significant effect in the investigated hematological markers when compared to their controls.Histological assessment of kidney and liver of ABG-001 treated mice revealed no significant changes as compared to control mice.Consequently,by evaluating hematological,biochemical,and histopathological effects of chronic treatment with ABG-001 in mice,we provide initial recommendation on the potential safety of this drug.Conclusions: Our study shows that ABG-001 alleviates oligodendrocyte damage through IGF-1R to relieve demyelination after chronic cerebral hypoperfusion,which might be represented as a promising treatment for SIVD.